I. Field
Aspects of the present invention relate generally to gamma ray sensors, and more particularly to methods and devices for detecting radioisotope concentration, activity and volume using gamma ray detection with cadmium zinc telluride (CZT) solid state detectors.
II. Background
Diagnostic techniques in nuclear medicine generally use radioactive tracers which emit gamma rays from within the body. These tracers are generally short-lived isotopes linked to chemical compounds which permit specific physiological processes to be studied. These compounds, which incorporate radionuclides, are known as radiopharmaceuticals, and can be given by injection, inhalation or orally. One type of diagnostic technique includes detecting single photons by a gamma-ray sensitive camera which can view organs from many different angles. The camera builds an image from the points from which radiation is emitted, and the image is electronically enhanced and viewed by a physician on a monitor for indications of abnormal conditions.
A more recent development is Positron Emission Tomography (PET), which is a more precise and sophisticated technique using isotopes produced in a cyclotron, where protons are introduced into the nucleus resulting in a deficiency of neutrons (i.e., becoming proton rich).
The nucleus of a radioisotope usually becomes stable by emitting an alpha and/or beta particle (or a positron). These particles may be accompanied by the emission of energy in the form of electromagnetic radiation known as gamma rays. This process is known as radioactive decay.
A positron-emitting radionuclide is introduced into the body of a patient, usually by injection, and accumulates in the target tissue. As the radionuclide decays, a positron is emitted, and the emitted positron combines with a nearby electron in the target tissue, resulting in the simultaneous emission of two identifiable gamma rays in opposite directions, each having an energy of 511 keV. These gamma rays are conventionally detected by a PET camera, and provide a very precise indication of their origin. PET's most important clinical role is typically in oncology, with fluorine-18 (F-18) as the tracer, since F-18 has proven to be the most accurate non-invasive method of detecting and evaluating most cancers. Fluorine-18 (F-18) is one of several positron emitters (including also, Carbon-11, Nitrogen-13, and Oxygen-15) that are produced in a cyclotron and are used in PET for studying brain physiology and pathology, in particular for localizing epileptic focus, and in dementia, psychiatry and neuropharmacology studies. These positron emitters also have a significant role in cardiology. F-18 in FDG (fluorodeoxyglucose) has become very important in detection of cancers and the monitoring of progress in cancer treatment, using PET. A radioactive product such as F-18 in FDG is a specific example of a radiopharmaceutical.
F-18 has a half-life of approximately 110 minutes, which is beneficial in that it does not pose a long-term environmental and/or health hazard. For example, after 24 hours, the radioactivity level is approximately 0.01% of the product when freshly produced in a cyclotron. However, transport time from the production source to clinical use should be minimized to retain a maximum potency for accurate diagnostic value.
Whereas PET cameras are effective in imaging uptake of F-18 present in administered FDG, PET cameras are generally too large and ineffective in production settings where characterization of the source product, and not physiological response, is the goal. There is a need, therefore, for a method and apparatus to timely calibrate the radioactivity of a sample at the production source and time of production or packaging for delivery so that the level of radioactivity is predictably known at the time of use.